A conventional receiver will be hereinafter described with reference to FIG. 4. In FIG. 4, conventional receiver 201 has first semiconductor chip 202 and second semiconductor chip 203 for diversity-receiving signals of a first radio frequency band, and a communication unit (not shown) for performing communication using signals of a second radio frequency band. First semiconductor chip 202 has the following elements:                first local oscillator 204 for oscillating first local signals;        first divider 205 for N-dividing the first local signals supplied from first local oscillator 204; and        first mixing unit 206 for frequency-converting the signals of the first radio frequency band using the first local signals supplied from first divider 205.Here, N is an integer of N>1. First semiconductor chip 202 has the following elements:        first filter 207 connected to the output side of first mixing unit 206; and        first-local-signal-output terminal 208 for outputting the first local signals supplied from first local oscillator 204 to the outside of first semiconductor chip 202.Second semiconductor chip 203 has the following elements:        first-local-signal-input terminal 209 for inputting the first local signals supplied from first-local-signal-output terminal 208 into second semiconductor chip 203; and        second divider 210 for N-dividing the first local signals supplied from first-local-signal-input terminal 209.Second semiconductor chip 203 has the following elements:        second mixing unit 211 for frequency-converting the signals of the first radio frequency band using the first local signals supplied from second divider 210; and        second filter 212 connected to the output side of second mixing unit 211.        
In conventional receiver 201, second mixing unit 211 of second semiconductor chip 203 performs frequency conversion using first local oscillator 204 of first semiconductor chip 202. Therefore, the power consumption of receiver 201 can be reduced.
An example of the conventional art document information related to the invention of this application is Patent document 1.
In this structure, the first radio frequency band can be separated from the frequency band of the first local signals, by setting dividing ratio N between first divider 205 and second divider 210 to be higher than 1. Thus, the possibility that the frequency of the first local signals comes into the first radio frequency band to cause obstruction can be reduced. The constant of inductance or capacitance of first local oscillator 204 can be decreased with increase in oscillating frequency of first local oscillator 204, namely increase in N. Therefore, first local oscillator 204 can be downsized.
When N is increased, however, the power consumption of first divider 205 or the like is increased. Signals of the second radio frequency band supplied from the communication unit come into first-local-signal-output terminal 208 and first-local-signal-input terminal 209, namely external terminals of respective semiconductor chips 202 and 203. Second mixing unit 211 originally frequency-converts the signals of the first radio frequency, but also frequency-converts the signals of the second radio frequency band coming from the communication unit. At this time, when the frequency of the signals of the second radio frequency band coming from the communication unit is close to a predetermined range from the frequency of the first local signals fed from first-local-signal-output terminal 208 into first-local-signal-input terminal 209, the frequency conversion by second mixing unit 211 causes the generation of disturbing signals that cannot be completely removed by second filter 212. This disturbing signal arises from signals of the second radio frequency band coming from the communication unit. As a result, the receiving quality of receiver 201 degrades, disadvantageously.
[Patent document 1] Japanese Patent Unexamined Publication No. 2005-130279